The video footage from a US Apache helicopter in 2007 posted by Wikileaks

The Afghan government said at the time that the strikes by F-18 and B1 planes near Granai killed 147 civilians. An independent Afghan inquiry later put the toll at 86.

Video footage of the strike could prove highly damaging to the Nato-led coalition if it showed pilots failing to safeguard civilian lives.

A harrowing videoshowing a US helicopter gunship crew killing a crowd of Iraqis including two journalists in Baghdad caused anger when it was published by Wikileaks last week.

An American inquiry into the May 4 Farah incident was only partially released and estimated that 26 died, but added: "no one will ever be able conclusively to determine the number of civilian casualties that occurred".

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The jets repeatedly dropped 500lb and 2,000lb bombs to support US and Afghan forces at they battled Taliban fighters and tried to evacuate wounded soldiers.

"The inability to discern the presence of civilians and avoid and/or minimise accompanying collateral damage resulted in the unintended consequence of civilian casualties," the US inquiry found.

A spokesman for the Nato-led coalition said: "All I have heard is the reports that they are going to release it." Employees of Wikileaks have said they are facing intimidation and attempts by intelligence services to shut them down after releasing a series of sensitive documents.